Chacin hasn't pitched since May 10, when he gave up five runs on six hits, including three home runs, in a three-inning start against Oakland. He left that start with a sore arm that turned out to be a strained ulnar collateral ligament, landing him on the 15-day disabled list.
But there was no sign of any lingering soreness on Monday, when Chacin played catch in the outfield, then moved into the bullpen for a 20-minute session.
Pitching coach Brad Arnsberg said that Chacin had thrown at about 80 percent in a weekend session in Colorado, then turned up the intensity on Monday.
"This time, we wanted to go out and air it out to really see where he was, and he was outstanding," said Arnsberg. "His sinker was real good, his cutter was real good and his curveball and changeup were all good."
Chacin may be ready, but the Blue Jays don't want to rush him back.
"We didn't give him a lot of time after the initial injury," Arnsberg said. "He was throwing again four days later, and that's kind of unusual on a mild strain of a ligament. To guard on the cautious side is best for us right now.
"We want to see this guy pitch in all of June, July, August and September rather than try to race him back. We've done it the right way so far, and to try to bring him back in the Chicago series is asking a lot of anybody. I don't think it's a matter of his arm not being ready -- it's a matter that we feel a bit more comfortable giving him a couple more days and letting him see some hitters."
Rotation roundup: With Chacin pushed back, rookie right-hander Casey Janssen will start on full rest against the White Sox on Saturday. Sunday's starter will either be Roy Halladay or Ty Taubenheim. Gibbons said that he may give Halladay an extra day off and hold him until the Red Sox arrive on Monday.
"An extra day here and there doesn't hurt anybody," he said. "Sometimes it does them good."
If Halladay does pitch on Sunday, the Jays will move Taubenheim into the bullpen. Toronto doesn't need a fifth starter this week because of Thursday's off-day.
Burnett bound for the mound: Injured starter A.J. Burnett has been throwing on flat ground for the past 10 days, and so far, he's been pain-free.
"He went to 110 feet yesterday and 110 feet and 40 throws today," said Arnsberg. "He'll take tomorrow off, and then the next two days, he'll back up to 120 feet."
In addition to the long-toss, Burnett is also throwing side sessions to maintain his delivery.
"He's moving along," said Gibbons. "By the end of the week -- I'm not sure which day -- he'll get on the mound in the bullpen, and we'll see where he's at."
Burnett has struggled since Sring Training with scar tissue and a strained ligament, and he has made just two appearances for the Jays this season.
Holiday Monday for Wells: It's a holiday weekend north of the border, as Canadians celebrate Victoria Day. Center fielder Vernon Wells also got the day off on Monday and was replaced by Alex Rios.
Gibbons said that he had planned to give Wells some rest after a nine-game road trip covering three time zones.
"With the time change and all that, and a day game today, it will beat you up a little bit," he said.
Coming up: The Blue Jays will send Halladay (5-1, 3.04 ERA) to the mound on Tuesday at 7:07 p.m. ET. Toronto's ace hasn't lost in six starts, but the only team to beat him this season is the Devil Rays, who won 5-2 on April 9 in Toronto.
The Rays will counter with former Jays lefty Mark Hendrickson (3-3, 3.57 ERA). The towering southpaw has made eight starts against his old mates, going 2-4.